The invention relates to a valve system for control of the rate of fluid flow, and in particular the invention relates to pilot operation of a main valve for such purposes.
In the past, it has been customary to rely upon a pressure-operated main valve to determine the range of flow rate for controlled delivery of pressure fluid, from a source to a given load, and a pilot valve has been associated with the main valve, analogous to a control amplifier, in order to develop control of actuating-pressure delivery to the main valve. In short, the range of the main valve was the range of the system, and the fidelity of system response suffered at the low-flow end of the range of the system.